<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Login Form</title>
    <style>
        body {
            margin: 0;
            padding: 0;
            background-color: #f0f0f0;
        }

        form {
            background-color: #fff;
            padding: 20px;
            border-radius: 5px;
            /* 请在此处添加代码，使表单在页面中居中显示 */
        }

        .form-group {
            margin-bottom: 15px;
        }

        label {
            display: block;
            margin-bottom: 5px;
        }

        input[type="text"], input[type="password"] {
            width: 100%;
            padding: 10px;
            border: 1px solid #ccc;
            border-radius: 3px;
            /* 请在此处添加代码，使输入框在获得焦点时边框颜色变化 */
        }
    </style>
</head>
<body>
    <form>
        <div class="form-group">
            <label for="username">Username:</label>
            <input type="text" id="username" name="username">
        </div>
        <div class="form-group">
            <label for="password">Password:</label>
            <input type="password" id="password" name="password">
        </div>
        <!-- 请在此处添加提交按钮 -->
    </form>
</body>
</html>